Must a day be made up after Ramadan to complete thirty days, if the people in Russia fast and break their fast according to the calendar without sighting the moon, and they issue fatwas that the duration of Ramadan is always 29 days, thus contradicting the possibility that Ramadan could be thirty days and the saying of the Prophet, peace and blessings be upon him: "The month is thus and thus"?

Determining the beginning and end of lunar months by astronomical calculation is not permissible. It contradicts authentic hadiths and the majority of scholars. The Islamic Fiqh Council has also decided against relying on it. The hadith "Eid al-Fitr is the day the people celebrate Eid al-Fitr, and Eid al-Adha is the day the people celebrate Eid al-Adha" is interpreted to mean that fasting and breaking the fast should be done with the Muslim community and the general populace. If your country relies on astronomical calculation, you should rely on your own sighting of the crescent moon if possible, or on the closest country that relies on legitimate sighting. If it becomes clear that Ramadan was thirty days, then you must make up the extra day.